Magnetic recording apparatus

ABSTRACT

In the sliding surface of a magnetic head to a magnetic tape, the center of a magnetic gap G is offset to the center CL of a core width so that the overwrite edge Ga of the magnetic gap G approaches the center CL of the core width. As a result, the data track left to a magnetic tape by overwrite is recorded with the portion of a magnetic head which is located at the center of cores and in good touch with the magnetic tape, whereby the recorded pattern of the data track is stable and the variation of a reproduced output can be suppressed.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a magnetic recording apparatusfor overwriting data on a magnetic recording medium with, for example, amagnetic head mounted on a rotary drum, and more specifically, to amagnetic recording apparatus for stabilizing the recorded state oftracks to which data is overwritten.

[0003] 2. Description of the Related Art

[0004] In magnetic recording apparatuses used in video equipment andmagnetic recording apparatuses for writing data for computers, amagnetic head is mounted on the rotary drum of a rotary head unit, and amagnetic tape travels in helical contact with the rotary drum as well asthe rotary drum rotates so that a recording operation is carried out tothe magnetic tape in a helical scan system.

[0005] Among this type of the magnetic recording apparatuses, there is amagnetic recording apparatus which uses a magnetic head having amagnetic gap whose track width Tw is larger than the pitch Tp of tracksrecorded on a magnetic tape and overwrites data to the magnetic tape byscanning the magnetic head so that the magnetic gap overwrites the trackof the magnetic tape where data is already written.

[0006]FIG. 5 is a plan view showing the tape sliding surface of themagnetic head mounted on the rotary drum of the magnetic recordingapparatus in an enlarged fashion.

[0007] A magnetic gap G is formed to a portion of the tape slidingsurface of the magnetic head where cores 1 and 2, which are formed of amagnetic material having a high magnetic permeability, are jointed inconfrontation with each other through a non-magnetic material layer.Although the magnetic gap G has an azimuth angle which is inclined by aminute angle with respect to a direction (X-direction) orthogonal to ascanning direction Y, the magnetic gap G is shown at a right angle withrespect to the scanning direction Y in this specification.

[0008] Symbol Tw denotes the track width of the magnetic gap G. Thetrack width Tw is determined by the depth of core regulating grooves 3,3 formed to a V-shape on both the right and left sides of the cores 1, 2at the portion where they are jointed to each other. In a magnetic gap Gwhich is actually formed with an azimuth angle, the track width Tw meansthe size between both the edges G1-G2 of the inclined magnetic gap G inthe track width direction (X-direction). Further, when the distancebetween the overwrite edge G1 of the magnetic gap G and the side edgesof the cores 1, 2 is denoted by symbol L1 and the distance between theother edge G2 and the side edges of the cores 1, 2 is denoted by symbolL2, L1=L2 is established in the magnetic head used in the conventionalmagnetic recording apparatus and the center of the track width Tw of themagnetic gap G matches the center CL of the cores 1, 2 in the widthdirection thereof.

SUMMARY OF THE INVENTION

[0009] When data is recorded by overwrite using the conventionalmagnetic head, a recorded pattern is made unstable on the track wheredata is recorded on a magnetic tape, and, in particular, data recordedby the portion of the overwrite edge G1 of the magnetic gap G is madeunstable. As a result, when overwritten magnetic information isreproduced, there arises problems such as a reproduced output is varied,and the like.

[0010] In particular, the pitch of tracks recorded on a magnetic tape isrecently made narrower to realize recording of a high density incorrespondence to the transfer of recorded data in a high density, andthere is proposed a recording format having a track pitch of about 10 μmor less. In the magnetic recording made using such a narrow track pitch,unstable recording of data in the overwrite edge G1 has a significanteffect as the variation of a reproduced output.

[0011] Reasons why the unstable recording is caused are as describedbelow.

[0012] Although the tape sliding surface of the magnetic head shown inFIG. 5 is formed to a curved shape in the scanning direction(Y-direction), it is also formed to a curved shape in the track widthdirection (X-direction). This is caused by that when the tape slidingsurface is polished in the scanning direction (Y-direction), it is alsoformed to the curved shape in the X-direction at the same time. Then,the apex of the curved surface in the X-direction approximately matchesthe center CL of the cores 1, 2 in the width direction thereof.

[0013] Since the center of the track width Tw of the magnetic gap Gapproximately matches the center CL of the cores 1, 2 in the widthdirection thereof, the overwrite edge G1 of the magnetic gap G islocated at a position apart from the center CL so that the overwriteedge G1 is located at a position which retreats in a direction where itis somewhat apart from the tape with respect to the apex of the curvedsurface at the center CL. As a result, the portion of the overwrite edgeG1 unstably touches the magnetic tape, whereby the recorded pattern ismade unstable and the reproduced output is varied.

[0014]FIG. 6 shows the state that magnetic data is overwritten to themagnetic tape with the magnetic head shown in FIG. 5.

[0015] In FIG. 6, symbol D1 denotes data initially recorded on themagnetic tape which is scanned with the magnetic gap G and a center CLin the core width direction at the time is denoted by symbol CL1. Next,symbol D2 denotes magnetic data recorded on the magnetic tape which isscanned with the magnetic gap G while partially overlapping the magneticgap G to the data D1 in a track width direction. The pitch Tp of a datatrack Dt which is left by overwrite is determined by the position of theoverwrite edge G1 of the magnetic gap G.

[0016] As shown in FIG. 6, the data track Dt which is left from theinitially recorded magnetic data D1 is data recorded at a portion of themagnetic head which is greatly apart from the center CL of the tapesliding surface of the magnetic head in the core width directionthereof. That is, the data which is recorded at the portion of themagnetic head where the magnetic gap touches the magnetic tape in a badstate is left as the data track Dt. In particular, a data boundary De inoverwrite is recorded with the edge G1 of the magnetic gap G which isgreatly apart from the center CL of the tape sliding surface in the corewidth direction thereof, data is liable to be unstably recorded at theboundary De.

[0017] An object of the present invention for solving the aboveconventional problem is to provide a magnetic recording apparatuscapable of suppressing the great variation of a reproduced output bystabilizing the recorded pattern of a data track left to a recordingmedium by overwrite.

[0018] A magnetic recording apparatus of the present invention forcarrying out an overwrite operation so that a magnetic gap having aprescribed track width overlaps the recording track having been recordedon the magnetic recording medium in the track width direction thereof byscanning a magnetic recording medium with a magnetic head to which themagnetic gap is formed at the portion thereof where cores composed of amagnetic material are confronted with each other is characterized inthat the magnetic gap is formed by being offset with respect to the corewidth in the magnetic head so that the overwrite edge of the magneticgap is offset to the center of the core width.

[0019] The magnetic recording apparatus of the present invention isarranged such that a magnetic head is mounted on the rotary drum of arotary head unit, a magnetic tape travels in helical contact with therotary head unit, the rotary drum is rotated and the magnetic tape ishelically scanned with the magnetic head. Otherwise, the magneticrecording apparatus is such that a magnetic head may scan a magnetictape in a plane fashion and overwrite may be carried out at the time oroverwrite may be carried out when a disc-shaped magnetic recordingmedium is scanned with a magnetic head.

[0020] More specifically, according to the present invention, it ispreferable that Tw−Tp=L1−L2 (however, L1>L2) is established, where Twrepresents the track width of the magnetic gap, L1 represents thedistance between the overwrite edge of the magnetic gap and the sideedges of the cores, L2 represents the distance between the edge of themagnetic gap opposite to the overwrite edge and the side edges of thecores, and Tp represents the track pitch of a data track left to themagnetic recording medium by being overwritten.

[0021] In particular, the present invention is effective when thesliding surface of the cores to the recording medium is formed to acurved shape so that the center (CL) in the core width becomes an apex.

[0022] In the present invention, since the magnetic gap is formed bybeing offset with respect to the core width in the magnetic head so thatthe overwrite edge of the magnetic gap is offset to the center of thecore width, the overwrite edge can be located at the portion of thesliding surface of the magnetic head which is in good touch with therecording medium. As a result, since the data track left to the magneticrecording medium by overwrite is recorded with the portion of themagnetic head which is in good touch with the magnetic recording medium,a recorded pattern is stable, and, as a result, a reproduced output isnot greatly varied.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023]FIG. 1A is an enlarged plan view showing the tape sliding surfaceof a magnetic head used to a magnetic recording apparatus of the presentinvention and FIG. 1B is a sectional view of the tape sliding surface;

[0024]FIG. 2 is a plan view showing the overwritten pattern of amagnetic tape in the magnetic recording apparatus of the presentinvention;

[0025]FIG. 3 is a perspective view of the magnetic head;

[0026]FIG. 4 is a front elevational view showing the rotary head unit ofthe magnetic recording apparatus of the present invention;

[0027]FIG. 5 is an enlarged plan view showing the tape sliding surfaceof a conventional magnetic head;

[0028]FIG. 6 is a plan view showing an overwritten pattern recorded withthe magnetic head shown in FIG. 5;

[0029]FIG. 7A is a view explaining a data track recorded on a magnetictape in an embodiment when it is observed with an MFM and FIG. 7B is aview explaining a data track recorded on a magnetic tape in acomparative example when it is observed with the MFM; and

[0030]FIG. 8A is an envelope waveform view when recorded data isreproduced in the embodiment and FIG. 8B is an envelope waveform viewwhen the recorded data is reproduced in the comparative example.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0031]FIG. 1A is an enlarged plan view showing the tape sliding surfaceof a magnetic head, FIG. 1B is a sectional view of the sliding surfaceof the magnetic head, FIG. 2 is an explanatory view explaining anoverwrite operation executed using the magnetic head, FIG. 3 is aperspective view showing an example of the magnetic head, and FIG. 4 isa front elevational view showing the rotary head unit of a magneticrecording apparatus on which the magnetic head is mounted.

[0032] A fixed drum 11 A is fixed in a rotary head unit 10 disposed tothe magnetic recording apparatus shown in FIG. 4, and a rotary drum 12which is coaxial with the fixed drum 11 is rotatably supported on thefixed drum 11 and rotated in the direction of an arrow by a motor. Amagnetic tape T as a magnetic recording medium travels while drawing ahelical locus in the direction of the arrow by being wound around therotary head unit 10 at a prescribed angle. While the magnetic tape Ttravels, the rotary drum 12 is rotated and a magnetic head H mounted onthe rotary drum 12 scans the magnetic tape T so that overwrite iscarried out to the magnetic tape T as shown in FIG. 2.

[0033] As shown in FIG. 3, the magnetic head H has cores 21, 22 formedof a magnetic material having a high magnetic permeability such asferrite or the like.

[0034] On the sliding surface of the magnetic head H on which themagnetic tape T slides, a magnetic gap G is formed to a portion of thesliding surface where the core 21 confronts the core 22 with a magneticmaterial layer interposed therebetween. Recording/reproducing coils 23,24 are wound around the cores 21, 22. Further, V-shaped gap regulatinggrooves 25, 26 are formed to the cores 21, 22 on both the sides thereofon the sliding surface so as to define the track width Tw of themagnetic gap G. The gap regulating grooves 25, 26 are filled with a wearresistant non-magnetic material, for example, SiO₂.

[0035]FIG. 1A shows the track width of the magnetic gap G is denoted bythe symbol Tw. Although the magnetic gap G usually has an azimuth anglewhich is inclined by a minute angle with respect to an X-directionorthogonal to the sliding direction (Y-direction) of the magnetic tapeT, the azimuth angle is set to zero in FIG. 1A. When the magnetic gap Ghas an azimuth angle, the track width Tw is the distance between theedges Ga, Ga of the magnetic gap G in the core width direction(X-direction) thereof.

[0036] As shown in FIG. 1A, the center of the magnetic gap G in thetrack width Tw direction thereof is formed by being offset to the centerCL of the cores 21, 22 in the width direction thereof so that theoverwrite edge Ga of the magnetic gap G is offset to the above center CLon the sliding surface of the magnetic head H.

[0037] As shown in FIG. 3, although the sliding surface of the magnetichead H is polished to an approximately cylindrically curved shape in thescanning direction (Y-direction), it is formed to an approximatelycylindrically curved shape also in the X-direction by the polishing jobas shown in FIG. 1B. Then, the apex of the curved surface in theX-direction approximately matches the center CL in the core widthdirection.

[0038] Since the magnetic gap G is formed at the offset position asdescribed above, the overwrite edge Ga of the magnetic gap G is locatedat a portion which is near to the apex on the curved shape in theX-direction.

[0039] The distance between the overwrite edge Ga of the magnetic gap Gand the side edges of the cores 21, 22 is denoted by symbol L1 and thedistance between the other overwrite edge Gb of the magnetic gap G andthe side edges is denoted by symbol L2. Further, when the track pitch ofa data track Dt which is left to the magnetic tape T as a result of theoverwrite shown in FIG. 2 is denoted by a symbol Tp, Tw−Tp=L1−L2(however, L1>L2) can be established.

[0040] A recording operation using the magnetic recording apparatus willbe described.

[0041] As shown in FIG. 4, the magnetic tape T as the magnetic recordingmedium travels in the direction of the arrow by being wound around therotary head unit 10 and the rotation of the rotary drum 12 permits themagnetic head H to scan the recording surface of the magnetic tape T todraw a helical locus. As shown in FIG. 2, magnetic data D1, D2, D3 . . .are sequentially overwritten on the recording surface of the magnetictape T by the feed speed of the magnetic tape T and the scanningperformed by the magnetic head H.

[0042] Although the respective magnetic data D1, D2, D3 . . . arerecorded with a width corresponding to the track width Tw of themagnetic gap G of the magnetic head H, when other data is overwritten onthem, the region located between the recorded portions of the overwriteedges Ga of the magnetic gap G are left to the magnetic tape T as thedata track Dt.

[0043] As shown in FIG. 1A and FIG. 1B, since the overwrite edge Ga isoffset to the center CL of the cores 21, 22 in the width directionthereof on the sliding surface of the magnetic head H, the portion towhich magnetic recording is carried out in the region (or region near tothe above region) which includes the center CL (the apex on the curve inthe X-direction) on the sliding surface of the magnetic head H is leftas the data track Dt. In FIG. 2, the centers in the core width directioncorresponding to the magnetic data D1, D2, D3 . . . are denoted bysymbols CL1, CL2, CL3, . . . . As shown in FIG. 2, the center CL in thecore width direction is located at an approximately mid portion of thedata track Dt written at the track pitch Pt.

[0044] As described above, since there is left, as the data track Dt, amagnetically recorded region where data is recorded in the state thatthe magnetic tape is in good touch with the sliding surface of themagnetic head, the magnetically recorded pattern in the region left asthe data track Dt is stabilized, and, in particular, the data boundaryDe of the data track Dt written at the edge Ga is stabilized.Accordingly, when the data is reproduced by the magnetic head, thevariation of the reproduction output of the data is reduced.

[0045] Magnetic data was recorded on an 8 mm VTR magnetic tape T using amagnetic recording apparatus on which an 8 mm VTR magnetic head H wasmounted. The track width Tw of the magnetic head H was set to 20 μm andthe pitch Tp of a data rack was set to 5 μm. The traveling speed of themagnetic tape T was set to 3.8 m/sec and the frequency of a recordingsignal was set to 10 MHz.

[0046] In an embodiment, a core width (Tw+L1+L2) was set to 55 μm, L1was set to 25 μm and L2 was set to 10 μm. In a comparative example, acore width was 55 μm, L1=L2, and L1 and L2 were set to 17.5 μm,respectively.

[0047]FIG. 7A shows a result of observation when a recorded patternrecorded by the embodiment was observed under a magnetic forcemicroscope (MFM), whereas FIG. 7B shows a result of observation when arecorded pattern recorded by the comparative example was observed underthe MFM. FIG. 8A is an envelope waveform view when the magnetic datarecorded by the embodiment was reproduced, whereas FIG. 8B is anenvelope waveform view when the magnetic data recorded by thecomparative example was reproduced. In FIG. 8, the abscissa represents atime and the ordinate represents an envelope output level graduated by 5dB.

[0048] In the comparative example, the recorded pattern is disturbed inthe data boundary De as shown in FIG. 7B, whereas in the embodiment, therecorded pattern is not almost disturbed in the data boundary De asshown in FIG. 7A.

[0049] In the comparative example, the variation (i) of a reproducedoutput of about 1 dB which corresponds to the disturbance of therecorded pattern at the data boundary De is generated to the envelope asshown in FIG. 8B, whereas no extreme variation of a reproduced output isgenerated in FIG. 8A and the reproduced output is stable.

[0050] As described above, according to the present invention, when adata track is formed by overwrite, since the portion which is left asthe data track is written with the portion the magnetic head at thecenter in the width direction thereof which is good touch with amagnetic tape, a recorded pattern is made stable and a reproduced outputis not extremely varied.

What is claimed is:
 1. A magnetic recording apparatus for carrying outan overwrite operation so that a magnetic gap having a prescribed trackwidth overlaps the recording track having been recorded on the magneticrecording medium in the track width direction thereof by scanning amagnetic recording medium with a magnetic head to which the magnetic gapis formed at the portion thereof where cores composed of a magneticmaterial are confronted with each other, wherein the magnetic gap isformed by being offset with respect to the core width in the magnetichead so that the overwrite edge of the magnetic gap is offset to thecenter of the core width.
 2. A magnetic recording apparatus according toclaim 1 , wherein the sliding surface of the cores to the recordingmedium is formed to a curved shape so that the center CL in the corewidth becomes an apex.
 3. A magnetic recording apparatus according toclaim 1 , wherein Tw−Tp=L1−L2 (however, L1>L2) is established, where Twrepresents the track width of the magnetic gap, L1 represents thedistance between the overwrite edge of the magnetic gap and the sideedges of the cores, L2 represents the distance between the edge of themagnetic gap opposite to the overwrite edge and the side edges of thecores, and Tp represents the track pitch of a data track left to themagnetic recording medium by being overwritten.
 4. A magnetic recordingapparatus according to claim 3 , wherein the sliding surface of thecores to the recording medium is formed to a curved shape so that thecenter CL of the core width becomes an apex.